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The difference is that the more common one during the Civil War, the NA112, had the upper fluke of the anchor behind the left wing, whereas the NA113 had the upper fluke of the anchor in front of the left wing.
These types were used right up through WWII, although the NA112 type became much less common after the Civil War.(source: , by Alphaeus H.
The eagle appeared on many of the general staff buttons, but not on the Confederate general service nor the letter buttons.
They were beautiful buttons, most had the familiar eagle & anchor, some of the earlier ones had only an anchor.
Some were American made, but there were many beautiful British made buttons too. As quoted on the US Coast Guard website source listed below, “The service received its present name in 1915 under an act of Congress that merged the Revenue Cutter Service with the U. Life-Saving Service, thereby providing the nation with a single maritime service dedicated to saving life at sea and enforcing the nation's maritime laws.
The Coast Guard began maintaining the country's aids to maritime navigation, including lighthouses, when President Franklin Roosevelt ordered the transfer of the Lighthouse Service to the Coast Guard in 1939.
In 1946 Congress permanently transferred the Commerce Department's Bureau of Marine Inspection and Navigation to the Coast Guard, thereby placing merchant marine licensing and merchant vessel safety under its purview.” (sources: , by Alphaeus H.
The one on the left is a 3-piece “staff” button, a button made from three main parts – the front, the back, and a ring, or rim, connecting the front to the back.
The other button is referred to as a 2-piece button, the back, and the front which is made so that it wraps around the outer edges of the back.
There were many military schools, both during and after the Civil War, that had their own distinctive uniform buttons.
There are some very desirable Southern Civil War era school buttons.
I listed some good reference books in the first post. There is a very rare version of the eagle and horizontal anchor, with the anchor pointing the opposite direction from those worn during the Civil War through to the present. According to Tice, “Less than ten specimens of this button made around 1835-1855 have been found by the author.”(sources: Earlier US Navy buttons worn prior to the Civil War, made from the 1830’s to the early 1850’s, were of a design with the familiar eagle and anchor as with later designs, but the anchor was upright.